Spraying electrode for electrostatic separators formed by a support of non-conductive materials with a fabric of crossed and twisted threads of carbon fibers on its outer side and use of the spraying electrode

ABSTRACT

A discharge electrode for electrostatic precipitators has a support composed of an electrically non-conductive material, a fabric composed of crossed and twisted threads and disposed on an exterior of the support, the support having an upper end and a lower end, and further comprising an additional layer of a synthetic elastomer which covers at least one of the ends over a length of 400-600 mm. Also, an electrostatic precipitator for treatment of exhaust gasses containing SO 2 , SO 3 , HF or HCL is proposed with the new discharge electrode.

BACKGROUND OF THE INVENTION

The invention relates to a discharge electrode for electrostaticprecipitators, which consists of a support of non-conductive materialson whose exterior a fabric of crossed and twisted threads of carbonfibers is disposed, and to the use of the discharge electrode.

Various types of electrodes are known. Discharge electrodes andprecipitation electrodes, which are made of carbon, are described inDE-OS 28 51 757 and DE-AS 23 11 468. The carbon is employed there in theform of fabrics, felts and threads.

A precipitation electrode for electric precipitators, which has a foilof carbon permanently connected with a support on its electricallyconducting surface, is described in DE-PS 25 00 888. The carbon foil ismade of pressed graphite, while the support can consist of a plasticmaterial.

An electrode consisting of an electrically conducting support, on whicha fiber material made of a dielectric substance is disposed, isdescribed in EP 0 031 623 A1.

An acid-resistance discharge electrode for electric filters is describedin DE-GB 1 694 459, which consists of an acid-resistant non-metallicsupport body and an acid-resistant metal as the discharge member,wherein metal foils, in particular of noble metals, are disposed on thesupport body in such a way that the foils form discharge peaks ordischarge edges on the surface of the support body.

An electrode consisting of a perforated support on whose surface carbonis disposed is described in U.S. Pat. No. 1,130,215. In this case thecarbon is employed in powder form and forms discharge peaks on theexterior.

A device for the removal of solid or liquid particles from a gas flow isdescribed in DE-OS 25 18 952, wherein the gas flow is guided through aseparating chamber which is delimited by two electrodes disposedopposite each other, and wherein an electrical field is generatedbetween the electrodes, which is of such strength that essentially noionization takes place in the gas flow. At least one of the electrodesof this device is provided with a coating consisting of a fiber materialwith limited electrical conductivity and having a large number ofprotruding thin fibers. The coating here can consist of asbestos fibers,glass fibers, textile fabric, stainless steel or fine metal fibers whichare embedded in a plastic support.

SUMMARY OF THE INVENTION

The object on which the invention is based is to provide a dischargeelectrode which is corrosion-resistant and which at the same timepermits an electrostatic charge of the solid and/or liquid particlescontained in the gas in the corona for electrostatic precipitation.

In keeping with these objects and with others which will become apparenthereinafter, one feature of the present invention resides, brieflystated, in a discharge electrode for electrostatic precipitators whichhas a support of non-conductive materials with a fabric of crossed andtwisted threads of carbon fibers arranged in its outer side, wherein inaccordance with the present invention the upper end and/or the lower endin a length of 400-600 mm are covered with an additional layer withsynthetic elastomers. In this case the support is made in anadvantageous manner of plastic materials or caoutchouc. In anadvantageous manner the carbon fibers are made of graphite and have adiameter between 5 and 10 μm. Dry or wet operating electric filters canbe employed as electrostatic precipitators. It has been shown in asurprising manner that the fabric made of crossed and twisted threads ofcarbon fibers and disposed on the exterior of electricallynon-conduction materials makes possible a corona, by means of whichsolid or liquid particles contained in the exhaust gas areelectrostatically charged and precipitated at the precipitationelectrodes. The discharge electrode is markedly corrosion-resistant andis therefore suited for relatively long working periods.

A preferred embodiment of the invention consists in that the threadsrespectively consist of 2400 to 2600 carbon fibers. It is possible tocreate the fabric from these thread in a relatively simple manner bymeans of the bobbin lace method. The bobbin lace method is understood tobe the patterned crossing and twisting of twined threads, which as arule today is automatically performed with modern machines. If thethreads consist respectively of 2400 to 3600 carbon fibers, the effectof the individual fabric sections as discharge peaks is increased and ahomogeneous formation of the corona is made easier.

In accordance with a further preferred embodiment of the invention thefabric has an average thickness between 0.3 to 0.7 mm. Because of thisstep the exterior of the discharge electrode has a relatively greatmechanical stability.

A further preferred embodiment of the invention consists in that thesupport has a core of aramid. Aramids are understood to be the aromaticpolyamides of aromatic diamines and arylene dicarboxylic acids. Thetensile strength of the discharge electrode is considerably increased ina relatively simple manner if the support contains a core of aramid, sothat the arrangement of weights, which as a rule are 2 to 5 kg, can takeplace relatively quickly, and the discharge electrode can be employed inan advantageous manner even at particularly high gas velocities.

In accordance with a further embodiment of the invention the core has acircular cross section with a diameter of 1 to 3 mm. A core with acircular cross section of a diameter of 1 to 3 mm can be worked into thesupport in a relatively simple manner. This simplifies the production ofthe discharge electrode, wherein a relatively great tensile strength ofthe discharge electrode can be simultaneously achieved.

In accordance with a further preferred embodiment of the invention thesupport or the unit of core and support has a circular cross section ofa diameter of 5 to 10 mm. This step makes an even arrangement of thefabric of crossed and twisted threads of carbon fibers on the outside ofthe support possible, wherein it is simultaneously possible to form aneven corona over the entire effective length of the discharge electrode.

Butyl caoutchouc, for example, can be employed as synthetic elastomer.The synthetic elastomers can be applied by vulcanization on the upperand/or lower end. As a rule, spark erosion often occurs at the upperand/or the lower end of discharge electrodes because of the field andreduces the precipitation output of the electrostatic precipitator. Ifthe upper end and/or the lower end are enclosed over a length between400 and 600 mm with an additional layer of a synthetic elastomer, thisundesired spark erosion can be prevented and the efficiency of theelectrostatic precipitator can be increased.

In accordance with a further embodiment of the invention the lowerportion of the lower end has at least one protrusion crosswise inrespect to the longitudinal axis of the discharge electrode. This stepallows a relatively simple application of weights for stabilizing thedischarge electrode.

In accordance with a further preferred embodiment of the invention theupper end has an eye. In this way it is possible to arrange thedischarge electrode relatively easily in the electrostatic precipitator.This step also allows a relatively problem-free retrofitting ofelectrostatic precipitators by means of the additional simpledisposition of further discharge electrodes, which might be possiblyrequired if the values of the exhaust gases to be treated fluctuate to agreater extent.

Finally, an object of the invention is the use of the dischargeelectrode for the treatment of exhaust gases containing SO₂ or SO₃ or HFor HCl or mixtures thereof in electrostatic precipitators. In this caseit is advantageous that it is possible to free larger amounts of exhaustgases, containing SO₂ or SO₃ or HF or HCl or mixtures thereof, of theharmful acid substances, and that the discharge electrode does not showcorrosive damage because of SO₂ or SO₃ or HF or HCl or mixtures thereof.

The novel features which are considered as characteristic for thepresent invention are set forth in particular in the appended claims.The invention itself, however, both as to its construction and itsmethod of operation, together with additional objects and advantagesthereof, will be best understood from the following description ofspecific embodiments when read in connection with the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a longitudinal sectional view through the dischargeelectrode for electrostatic precipitators.

FIG. 2 shows the discharge electrode for electrostatic precipitators ina cross-sectional view along the section A--A in FIG. 1.

DESCRIPTION OF PREFERRED EMBODIMENTS

The discharge electrode for electrostatic precipitators is shown in alongitudinal sectional view in FIG. 1. The discharge electrode isdivided into an upper end a, a central element b and a lower end c. Thecentral element b is used to form the corona required for theelectrostatic precipitation. A core (1) surrounded by a support (2) isdisposed centered in the discharge electrode. The core (1) preferablyconsists of aramid. The support (2) preferably consists of syntheticelastomers. A fabric (3) of crossed and twisted threads made of carbonfibers is disposed on the outside of the electrically non-conductivesupport (2). The upper end a and the lower end c are covered with anadditional layer (4) of synthetic elastomers. A protrusion (5) crosswisein respect to the longitudinal axis of the discharge electrode isdisposed at the lower portion of the lower end c. Weights can bedisposed in a relatively simple manner on this protrusion (5). The upperend a has an eye (6), by means of which the discharge electrode can bedisposed in a relatively easy manner in the upper part of theelectrostatic precipitator

The cross section of the discharge electrode in accordance with thesection A--A in FIG. 1 is represented in FIG. 2. An electricallynon-conducting support (2) is arranged around the core (1), whichpreferably is made of aramid. The unit of core (1) and support (2) has acircular cross section. A fabric (3) of crossed and twisted threads ofcarbon fibers is disposed on the exterior of the support (2).

The invention will be described in detail below by means of an exampleand a comparative example.

EXAMPLE

The exhaust gas created in the course of the combustion of garbage has atemperature of 78° C., a dew point of 78° C., a dust content of 2 g/m³and occurs in an amount of 30,000 m³ /h. Small amounts of SO₂, SO₃, HFand HCl are furthermore contained in the exhaust gas. The precipitationsurface of the electrostatic precipitator is 500 m², whereinplate-shaped precipitation electrodes are utilized, which are disposedat a distance of 300 mm. Discharge electrodes are disposed in thecenters between the plate-shaped precipitation electrodes at a distanceof 400 mm from each other and have a total length of 5 m, while thecenter part has a length of 4.2 m. A core of aramid of a diameter of 2mm is disposed centered in each discharge electrode. A support ofsynthetic elastomers is arranged around the core of each dischargeelectrode. The unit of core and support of each discharge electrode hasa circular diameter of 8 mm. A fabric of crossed and twisted thread ofcarbon fibers is disposed on the exterior of each support. The fabrichas a thickness of 0.5 mm. The upper ends and the lower ends of theindividual discharge electrodes are enclosed with an additional layer ofsynthetic elastomers over a length of 0.5 m. The lower parts of thelower ends have a protrusion crosswise in respect to the longitudinalaxis of the discharge electrode, on which a respective weight of 3 kg isdisposed. The upper ends of the discharge electrodes have an eye, whoseinterior diameter is 11 mm and which is used to suspend the individualdischarge electrodes. With a field strength in the range between 2 to 4kV/cm, following the treatment of the exhaust gas a residual content of<10 mg/Nm³ of dustlike materials was measured in the clean gas. Theworking period of the discharge electrodes can be up to four yearswithout disadvantageous effects on the efficiency of the electrostaticprecipitator being noted.

Comparative Example

An exhaust gas of the same composition as in the above example istreated under the same conditions in the same electrostaticprecipitator. However, in contrast to the discharge electrodes recitedin the example, discharge electrodes made of wires of noble metals aredisposed in the electrostatic precipitators and centered between theplate-shaped starting sheets at the same distance as in the recitedexample. In contrast with the above example, the residual content ofdustlike materials in the clean gas following treatment of the exhaustgas was 30 mg/Nm³.

Thus, the discharge electrode for electrostatic precipitators inaccordance with the invention also makes possible, besides its simplehandling and corrosion resistance, an increase in the efficiency of theelectrostatic precipitator, the cause of which is the even formation ofthe corona in the center part of the discharge electrode.

We claim:
 1. A discharge electrode for electrostatic precipitators,comprising a support composed of an electrically non-conductivematerial; a fabric composed of crossed and twisted threads and disposedon an exterior of said support, said support having an upper end and alower end; and further comprising an additional layer of a syntheticelastomer which covers at least one of said ends over a length of400-600 mm.
 2. A discharge electrode as defined in claim 1, wherein saidadditional layer covers each of said ends over a length of 400-600 mm.3. A discharge electrode as defined in claim 1, wherein each of saidthreads consists of 2400-3600 carbon fibers.
 4. A discharge electrode asdefined in claim 1, wherein said fabric has an average thickness of0.3-0.7 mm.
 5. A discharge electrode as defined in claim 1, wherein saidsupport has a core composed of aramid.
 6. A discharge electrode asdefined in claim 1, wherein said support has a core with a circularcross-section having a diameter of 1-3 mm.
 7. A discharge electrode asdefined in claim 1, wherein said support has a circular cross-sectionwith a diameter of 5-10 mm.
 8. A discharge electrode as defined in claim1, wherein said support has a core and together with said core forms aunit with a circular cross-section having a diameter of 5-10 mm.
 9. Adischarge electrode as defined in claim 1, wherein said lower end has alower part provided with at least one projection which extendstransversely to a longitudinal axis of said support.
 10. A dischargeelectrode as defined in claim 1, wherein said upper end has an eye. 11.An electrostatic precipitator for treatment of exhaust gasses containinga substance selected from the group consisting of SO₂, SO₃, HF and HCL,the electrostatic precipitator comprising a discharge electrode having asupport composed of an electrically non-conductive material; a fabriccomposed of crossed and twisted threads and disposed on an exterior ofsaid support, said support having an upper end and a lower end; andfurther comprising an additional layer of a synthetic elastomer whichcovers at least one of said ends over a length of 400-600 mm.